Abstract
As the increase of the growing demand of information, it requires huge data capacity in data centers. Optical network systems with lower cost and higher capacity is used to support intra and inter data center connections. The distance is in the range from hundred meters to kilometers. Relative to binary signal, 4-ary pulse amplitude modulation (PAM4) can double the data rate and offers higher spectral efficiency. The main purpose of this study is to increase the transmission distance of PAM4 signals in and among data centers. One method is to achieve the distance is applying Decision Feedback Equalizer (DFE) in the receiver of an optical PAM4 system, and the other method is to employ an optical duobinary PAM4 signal format which half-reduces communication bandwidth. We experimentally demonstrate a 50 Gb/s PAM4 system with a 2-tap Decision Feedback Equalizer (DFE) and hard decision. The BER performance are evaluated with different transmission scenarios without and with DFE respectively. A 10-km single mode fiber (SMF) transmission is achieved by using DFE. In addition, we experimentally evaluate the chromatic dispersion tolerance of a duobinary PAM4 signal for data center communication. In comparison of ordinary PAM4, the duobinary PAM4 has higher dispersion tolerance without any physical or digital compensation, but it requires more receiving SNR. We also discuss the SNR requirement of duobinary PAM4 in comparison with ordinary PAM4.